Network switches are commonly enclosed within a chassis for support, physical security and efficient usage of space. The electronic components contained within the chassis generate a significant amount of heat. Thermal damage may occur to the electronic components unless the heat is removed properly.
Proper removal of the heat requires fans that draw low temperature air into the switch chassis from one side and push out the heated air on another side of the chassis. What is important for proper cooling is that cool air is available from the environment and that there is no re-circulation of heated air back into the chassis since this could result in less effective heat transfer and could cause the switch to overheat and potentially sustain thermal damage.
Network switches are typically installed in standard data center equipment racks, also known as 19″ racks. Historically most network switches were mounted with their switch ports facing to the front of the rack and have used side-to-side air cooling, where fans move air across the width of the switch, orthogonal to the plane of the switch ports, or have used side-to-rear air cooling, where air is drawn into the chassis from one or both sides of the chassis and pushed out to the rear of the chassis.
The conventional side-to-side or side-to-rear airflow design for network switches poses significant problems when deploying high performance networking switches in conjunction with rack-mounted servers or storage units that use front-to-back cooling, where air flows from the front of the chassis to the rear of the chassis. Using side-to-side or side-to-rear airflow network switches in the same rack as front-to-rear airflow servers creates hot air recirculation and potential overheating for the networking switch. In addition, server equipment racks are typically enclosed on the left and right side, leaving very little room inside the rack to supply cool air and remove heated air for switches that use side-by-side airflow cooling. Finally, server equipment rack enclosures are typically arranged in alternating hot and cold aisles, with the airflow direction from the cold to the hot aisle. Networking chassis with side-to-side or side-to-rear airflow are not compatible with the airflow created by the hot-and-cold aisle arrangement.
Side-to-side or side-to-rear airflow has cooling limitations within the networking chassis itself, in particular for high-performance switches that use optical lasers and/or other high power physical layer components. Cooling a large number of such high-power physical layer components with side-to-side airflow that is orthogonal to the layout of these components creates a significant air temperature rise that negatively affects the reliable operation of such components.
Cooling fans are generally the least reliable component in a networking chassis. Switches suitable for use in data center deployment typically must be continuously available, even if a fan has failed, and it is very desirable to be able to replace failed fans without affecting the network switch operation. It is very difficult if not impossible to provide hot-swappable redundant cooling in a switch chassis that uses side-by-side airflow.
Another problem is that two different orientations are used for mounting network switches in data center equipment racks. Conventionally network switches are installed with the networking ports facing to the front of the rack to allow for easy access to the network ports. However, if a network switch is deployed in the same rack as servers and the switch ports primarily connect to the server I/O ports, it is preferable to mount the switch such that the switch ports face to the rear of the rack since the server I/O ports are on the rear as well. This simplifies the cabling to the servers and minimizes the length of the cables required. Orientating the switch this way is sometimes referred to as “reverse mounting” in the sense that the front of the switch is now facing to the rear. Reverse mounting, however, necessitates a reversal of the airflow, i.e., the airflow direction for reverse mounting must go from the rear of the switch chassis to the front of the network switch chassis in order to be compatible with the airflow of the servers in the same rack. This ordinarily would require a different switch design in order to provide the appropriate airflow direction.